1. Field of the Invention
This invention relates to laminates used in glazing applications. This invention particularly relates to laminates useful as acoustic glazing for sound dampening.
2. Description of the Related Art
Glass laminates having sound-damping properties have found use in architectural applications as well as in vehicles. Such acoustic laminates are desirable to reduce sound transmission from external sources to the interior of a building or an automobile, for example.
Plasticized polyvinyl butyral (PVB) sheet is used in the manufacture of transparent laminate structures such as, for example: windshields for vehicles including automobiles, motorcycles, boats and airplanes, windows in buildings such as office buildings, apartment buildings, houses, and/or commercial buildings, for example.
In modern vehicles—particularly in trains, planes and automobiles—passenger comfort has become an important selling point in commercial transactions involving same. One important feature in a modern vehicle is the ability to minimize noise that originates from outside of the passenger compartment of the vehicle. Automobiles are particularly targeted for improving the acoustic quality of the passenger's ride. Noises coming from the engine compartment, from the sound of tires rolling across a road or the ground, and wind noise created as a car moves at rapid speed through air are all contributors to the noise generated as a car is used as it was intended.
Various improvements and modifications have been made to cars in order to improve the quietness of a passenger's travel. However, one major source of noise is sound that passes through the windows of a vehicle. The windows of a car are typically good conductors of sound waves—particularly at critical sound frequencies, that is, at sound frequencies that are perceptible to the human ear. Moreover, sound reduction in office and other buildings from noise emanating from outside of the building can be desirable in settings where outside noises can reach the level of distraction inside of a building.
Various patents describe inventive attempts to address the problem of noise reduction in vehicles and/or in buildings. U.S. Pat. No. 5,368,917 and U.S. Pat. No. 5,478,615 describe acoustic laminated glazings for vehicles comprising conventional polyvinyl butyral (PVB). U.S. Pat. No. 6,132,882 describes a sound-damping laminate comprising a vibration-damping layer such as a polyacrylate, at least one flexible plastic layer such as PVB, and a rigid glass or plastic sheet. U.S. Pat. No. 5,773,102 describes a soundproofing laminated glass pane wherein a high-performance acoustic film is combined with at least one film having ordinary acoustic performance, such as PVB. U.S. Pat. No. 5,190,826 describes interlayers for use in sound-insulating laminated glass. U.S. Pat. No. 6,074,732 describes a soundproofing laminated window made of two glass sheets between which are polymer layers in the order of PVB/PET/acrylate/PET/PVB. The PVB layers are conventional (that is, non-acoustic) PVB. U.S. Pat. No. 6,432,522 describes transparent laminates having sound attenuation properties comprising an interlayer film having at least two layers. WO 01/19747 A1 describes glass laminates wherein PVB is softened (plasticized) with 20 to 50 wt % of a two-component plasticizer mixture comprising 30 to 70 wt % of a polyalkylene glycol as one of the components. However, impact resistance of a laminate using softened PVB can be detrimentally affected.
Use of ethylene acid copolymers or salts thereof produce rigid interlayers which can be particularly useful as threat-resistant glazing units in automobiles and buildings. Imparting sound-dampening properties to such interlayers can be difficult because of the rigidity of these materials, and relative lack of adhesion to other interlayer materials with known acoustic properties such as, for example, PVB.
It can be desirable to have a laminate with sound dampening (sound-damping) properties that retains its impact resistance and resistance to penetration. It can be particularly desirable to have such properties in a threat-resistant glazing unit.